WASHINGTON (CNN) -- Oil giant Exxon Mobil Corp. has pleaded guilty and will pay $600,000 in fines for the deaths of 85 protected migratory birds in the company's wastewater ponds in five states.

Waterfowl, hawks and owls protected under an international treaty were killed after landing in uncovered pools, where they were coated with or ingested fatal doses of hydrocarbons, federal officials said.

The facilities are in Colorado, Wyoming, Kansas, Oklahoma and Texas.

"This is a great win for the environment," Acting Assistant Attorney General John Cruden told reporters in a telephone news conference.

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Justice Department lawyers announced that Exxon Mobil also agreed in a plea deal filed in federal court in Denver, Colorado, on Wednesday to spend millions of dollars to implement a three-year program to cover its natural gas well reserve pits and wastewater storage facilities.

A government lawyer said the law requires oil and gas companies to scrub the water of contaminants, remove the ponds, or place an obstruction such as plastic netting over the water to prevent birds from landing.

The government's environmental lawyers credited Exxon with fully cooperating after the issue was brought to the company's attention.

"They've already spent about $2.5 million and will spend quite a bit more to implement the environmental compliance plan," trial attorney Robert Anderson said.

The birds killed over a five-year period were identified by the U.S. Fish and Wildlife Service as ducks, grebes, ibis, passerines, shore birds, owls, martins and a hawk. None is listed as an endangered species.

The Justice Department said $400,000 of the fines will go to a wetlands conservation fund, and $200,000 in community service payments will be directed to waterfowl rehabilitation and preservation organizations.

The Migratory Bird Treaty Act signed by the United States, Canada, Mexico, Japan and Russia was enacted in 1918.